Compositionalism, Nestorianism, and the principle of no co-member parts

Abstract

Abstract Compositionalists hold that God the Son became human by acquiring all the parts that ordinarily compose a human being (his ‘human nature’). To be orthodox, though, they must deny that Christ's human nature is a person, even though it has all the parts that human persons ordinarily have. One way to do this is by appealing to the principle that no member of a natural kind can have another member of the same kind as a proper part. Since Christ is a person, he cannot have another person as a part, so if his human nature is a part of him, it cannot be a person. This principle is defended on the grounds that it can resolve metaphysical problems involving apparently multiple individuals of the same natural kind that share the same space. I argue that this is a weak strategy. First, it leaves unanswered key questions about how and why the principle applies to the incarnation. Second, counter-examples to the principle exist, suggesting that it is not true. Third, there is a better solution to the kinds of metaphysical paradoxes for which this principle is usually invoked, but this solution cannot be applied to the case of Christ. Consequently, compositionalists should not rely on this principle as a means of avoiding Nestorianism.